1. Field of the Invention
This invention relates generally to a fluid temperature sensor and more specifically to a fluid temperature sensor of the semiconductor type, the semiconductor chip being placed in a thin dome having a high surface area to mass ratio thereby providing an extremely fast acting temperature sensing unit.
2. Description of the Prior Art
As described above, the present invention relates to a temperature sensor which will provide a fast response device suitable for use in control systems where a rapid temperature sensing of a flowing fluid media is required. A typical use of such a temperature sensor would be in conjunction with the air induction system in an automotive engine wherein the air temperature is utilized in conjunction with other engine parameters for controlling the fuel in a fuel management system.
There are devices presently on the market which are similar to that which is to be described, but do not provide the extremely fast temperature response associated with the sensor of the present invention. In the temperature sensors presently being manufactured, for example by the Texas Instruments Corporation, the temperature sensing element is a silicon chip semiconductor which is doped by various impurities to control the resistance of the chip in response to variations in temperature. The silicon semiconductor chips are sized as blocks of approximately 0.015 .times. 0.015 .times. 0.006 inch dimension, the blocks being bonded to a metal plate on one side and a gold wire attached to the opposite side of the chip in typical semiconductor manufacturing fashion. The chip is then bonded to a metallic frame which is used as the base of the device, which frame is approximately 500 times the mass of the silicon chip. The entire assembly is then encased in a plastic molding for handling and installation strength.
The metallic frame utilized as the base of the device is of a thick cross-sectional area and relatively short in length thereby providing a low surface area to mass ratio. Further, the plastic incapsulant which has been made a structural part of the device has a low thermal conductivity compared to metal and thus impedes the flow of heat to or from the silicon chip. This incapsulant has been utilized due to the structural design of the assembly.
In two co-pending applications, commonly assigned, Ser. Nos. 857,558 and 857,559, filed Dec. 5, 1977, there is disclosed a fast response fluid temperature sensor wherein a semiconductor device is mounted on a relatively flat fin which is open on both sides to the fluid being sensed. In order to facilitate the connection of the silicon chip to the exterior conductors, a pair of fins are provided, the fins being generally dish-shaped to ensure air flow around the entirety of the assembly.
However, with the air flow flowing around the entire assembly, it is possible that, under certain circumstances, contaminants and other foreign material may cause damage to the chip and/or lead attached to the chip. It is this latter problem that the present invention addresses. The above-referenced co-pending disclosures are incorporated herein by reference.